In this post, I will try to explain why for the last 20 years or so I have taken it for granted that--at a level of abstraction required by discussion of religions as a whole--it is correct to say that Christians and Muslims do worship the same God.

To be clear, I am not claiming that Christianity and Islam are equivalent or that differences between these two religions are inconsequential. Nor am I suggesting that Christians and Muslims hold identical conceptions of God. My basic problem is with the way the differences are phrased: Stating that Christians and Muslims "do not worship the same God" implies that Christians and Muslims worship different gods. I am concerned about this issue not only because I am convinced that it is misguided on a theoretical level to state that Christians and Muslims worship different gods, but also because such a view is positively harmful when it comes to sharing the gospel with Muslims.

(1) Terminology: On Facebook, I wrote: "Do Christians and Muslims worship the same Allah? Of course they do. If
this conversation were being conducted in Arabic, there would be no
debate." The point of this provocative over-simplification--aside from registering my astonishment--was to observe that the two different names (Allah, God) may lead English-speakers to assume that the names refer to two different deities. I suspect this is what has happened on a popular level in North America. Ignorance and post-9/11 political realities, more than anything else, are why many evangelicals assume that Christians and Muslims worship different gods. But Allah, in Arabic, is the generic name for God. It was used by Christians before Islam began, it appears as the name for God in standard Arabic translations of the Bible, and it is still used by Arabic-speaking Christians today. If, as I will argue, it is correct to say that, despite their fundamental differences in theology, Christians and Muslims worship the same God, it is also true that they worship the same Allah.

(2) Similarities: Muslims and Christians agree that there is one God, and both Christians and Muslims describe the one God in many of the same ways: God, according to the Qur'an, is the creator, "the Mighty one, the All-knowing" (6.96); God is "the Lord of the Universe, the Compassionate, the Merciful" (1.2-3); God alone is "the Forgiving One" (15.49), etc. Muslim theology presents Islam as the correct continuation of God's revelation to Abraham, Jesus and the biblical prophets. As a result, when Muslims and Christians talk about God, they share a common starting point in a way that a Christian and a Hindu devotee of Krishna do not.

(3) Differences: To be sure, there are also significant differences. Built into Islam is a rejection of the deity of Jesus. From a Muslim perspective, Christians have fallen away from the true religion into tri-theism. For their part, Christians insist that any conception of God's oneness that denies God's self-revelation in Jesus is fundamentally distorted. These different conceptions of God must not be minimized. I would happily sign off on Wheaton's College's "Statement Regarding Christian Engagement with Muslim Neighbors":

While Islam and Christianity are both monotheistic, we believe there are
fundamental differences between the two faiths, including what they
teach about God’s revelation to humanity, the nature of God, the path to
salvation, and the life of prayer.

(4) Different Conceptions vs. Different Gods: Nevertheless, the fact that Christians and Muslims have different ideas about the
nature of God does not mean that they worship different gods. In this context, "different conceptions" is a meaningful statement; "different gods" is not:

Since both Christians and Muslims affirm that there is one God and that this God exists, we are talking about a concept with a real referent, not some abstract quality. Francis Beckwith explains:

Because, according to the classical theist, there can only in principle be one God, Christians, Jews, and Muslims who embrace classical theism must be worshipping the same God. It simply cannot be otherwise.

If Muslims who deny the deity of Jesus do not worship the same God as Christians, it follows that Jews do not worship the same God as Christians either. This is at the heart of the issue theologically: Denying that Christians and Jews worship the same God leads either to a Marcionite distinction between the God of the Old Testament and the God of the New or to a strong supersessionism that requires us to imagine Jews, en masse, becoming idolaters at the incarnation. (I exaggerate for effect.) Suffice it to say that you don't find the apostle Paul accusing his fellow Jews of idolatry. Instead, he says "they have zeal forGod, but not according to knowledge" (Rom 10:2). Different conceptions of the one God do not mean that the object of worship is different, and a fuller revelation of God's identity does not render earlier revelation obsolete--just incomplete.

Is it not the case that Christians too operate with false conceptions of God? What is to stop Calvinists from declaring that they worship a different God than Arminians, or Protestants than Catholics? Where do we draw the line--and why are we drawing it?

Instead of denying or minimizing the broad overlap in Christian and Muslim views about God, it is far better, in my view, to follow the example of Jesus in John 4, and Paul in Acts 17, and say "What you worship as unknown (or, in this case, partially known) I proclaim to you" (Acts 17:23; cf. John 4:22).

If you are interested in further reading on the subject, I recommend the following short articles written by Christians with years of experience working with Muslims:

About Me

But yield who will to their separation,
My object in living is to unite
My avocation and my vocation
As my two eyes make one in sight.
Only where love and need are one,
And the work is play for mortal stakes,
Is the deed ever really done
For Heaven and the future's sakes.
- Robert Frost, "Two Tramps in Mud Time"